14 



E. NOMUBA : 



the direct continuations of* those of the body wall, differing from the 

 latter only in the feebler development of the peritoneum and the 

 muscles. 



The pharynx commences at the beginning of the second seg- 

 ment and reaches to the end of the third. Its cavity is distinguished 

 from that of the mouth by the presence of cilia, as in most other 

 allied forms. In well narcotised specimens the lumen is flattened 

 dorso-ventrally and is very wide, except at the anterior part where 

 it is narrower from side to side. At the beginning it is A -shaped, 

 but passes into a semicircular form in the posterior part. The 

 pharyngeal wall consists apparently of two layers : the inner 

 endoderm of ciliated columnar cells and the outer peritoneal con- 

 nective tissue which contains fine blood- capillaries and feebly 



chl 





G> 



br 



Oesophagus 



Pharynx 



Buccal Cavity 



Fig. 9. 

 Schematised dorsal view of the anteriormost part of the alimentary canal (A) and 

 cross sections through its different parts ( K). xlOO. br— brain, through near the pos- 

 terior end, d.v— dorsal vessel, chl— chloragogue layer, sept — septum, pr — prostomium, nip 

 —median pharyngeal gland, lp— lateral pharyngeal gland, p.v — phryngeal vessel. 



developed muscle fibres. The endoderm is as thick as the hypodermis 

 of the buccal cavity at the beginning of the second segment, but 

 a little further backwards it is more or less suddenly thickened 

 and becomes about thrice as thick. The cytoplasm is compact and 



